1. Field of the Invention
This invention relates to the communications field, and more particularly to a tunable patch antenna that has a tuning range of up to 30% of the center frequency of operation fcenter, the latter being anywhere between about 30 MHz to 40 GHz.
2. Description of Related Art
Today there is a lot of research going on industry to develop a tunable patch antenna that can be electronically tuned to any frequency within a wide band of operation. One traditional tunable patch antenna is tuned by semiconductor varactor diodes but this antenna suffers from several problems including: (1) linearity problems; and (2) power handling problems. Another traditional tunable patch antenna is tuned by MEMS switches but this antenna suffers from several problems including: (1) power handling problems; (2) undefined reliability since the MEMS switches are mechanical devices suffering from fatigue after repetitive use; and (3) the resonant frequency of the antenna cannot be continuously scanned between two points, since the MEMS switches are basically binary devices. Yet another traditional tunable patch antenna is tuned by voltage-tunable edge capacitors and has a configuration as shown in FIGS. 1A and 1B.
Referring to FIGS. 1A and 1B (PRIOR ART), there are respectively shown a perspective view and a side view of a traditional tunable patch antenna 100 that is tuned by voltage-tunable edge capacitors 102. The tunable patch antenna 100 includes a ground plane 104 on which there is located a substrate 106 on which there is located a patch 108. The patch 108 has two radiating edges 110a and 110b on which there are attached multiple voltage-tunable edge capacitors 102 (six shown). In operation, a radio frequency (RF) signal 111 is applied to a RF feedpoint 112. And, a DC bias voltage 114 is applied to the patch and the voltage-tunable edge capacitors 102. The tunable patch antenna 100 has a resonant frequency at its lowest frequency when it is in an unbiased state or when no DC bias voltage 114 is applied to the voltage-tunable edge capacitors 102. But when a DC bias voltage 114 is applied to the voltage-tunable edge capacitors 102, then the voltage-tunable edge capacitors 102 change their electrical properties and capacitance in a way such that when there is an increase in the magnitude of the DC bias voltage 114 then there is an increase in the resonant frequency of the tunable patch antenna 100. In this way, the tunable patch antenna 100 can be electronically tuned to any frequency within a band of operation in a range of up to 15% of the center frequency of operation fcenter. FIG. 2 shows a graph of a theoretical input reflection [dB] versus frequency [GHz] for the tunable patch antenna 100. Although the traditional tunable patch antenna 100 works fine in most applications it would be desirable to have a tunable patch antenna that can be electronically tuned to any frequency within a larger band of operation which is in a range of up to 30% of the center frequency of operation fcenter. This need and other needs have been satisfied by the tunable patch antenna of the present invention.